As far as I can work out, the reason they're being used is to reassure the public and discourage flu sufferers from visiting airports and malls.

However, since they were shown in the SARS outbreak not to be effective in preventing transmission, the whole exercise seems pretty cynical. It relies on the public believing in a product that the authorities know to be useless. As the Wizard of Oz might say: "Pay no attention to that man behind the curtain!"